US3409902A - High speed thermal printer - Google Patents

Description

Nov. 5, 1968 J. o. MERRYMAN 3,4099% HIGH SPEED THERMAL PRINTER Filed May 27, 1966 4 Sheets-Sheet 1 INTERFACE DATA SOURCE NV ENTO R JERRY D. MERRYMAN ORNEY 1968 J. D. MERRYMAN HIGH SPEED THERMAL PRINTER 4 Sheets-Sheet 2 Filed May 27, 1966 m Om m M MR H mm wm M Wm m vw A W E X J xUO G ommam IO I WE mm om Nov. 5, 1968 J. D. MERRYMAN HIGH SPEED THERMAL PRINTER 4 Sheets-Sheet 5 Filed May 27. 1966 Vcc INVENTOR F G- 6 JERRY 0. MERRYMAN 1968 J. D. MERRYMAN HIGH SPEED THERMAL PRINTER 4 Sheets-Sheet 4 Filed May 27. 1966 L mwkwRv Em Cm 1 m6 15mg E56 Kim .5208

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V51"; E on United States Patent "ice ,HIGH SPEED THERMAL PRINTER l-Jerry D. Merryman, Dallas, Tex.,assignor to Texas Instruments Incorporated, Dallas, Tex., a corpoe ration of Delaware May 27, 1966, Ser. No. 553,420

Filed 6 Claims. (Cl. 34676) 3,409,902 Patented Nov. 5, 1968 of the periphery of the drum. Serial data is fed to the data converter means through slip rings and appropriate steering logic also carried by the drum' during the period when the paper is not in contact with the respective print heads to which the information pertains. The hot spots are then turned on in accordance with the data during the remainder of the revolution of the drum, and while in contact with the paper, each hot spot marks the heat sensitive paper to reproduce the data. A single channel may be used for input information, or a plurality of channels for the input information may be used in parallel to reduce the rate at which the serial information is supmemorymeans carried by the. rotating drum. The mem- I ory. means. receives serial data and converts the serial data to parallel data at a plurality of outputs associated withindividual heating elements to produce preselected patterns of heated elements.

This invention relates generally to thermal printing, and more particularly relates to a high speed thermal print head suitable for use as a readout system for digital data storage and processing systems, and the like.

There are a great many applications forhigh speed printing devices. For example, the speed of many computers and data handling systems is limited by the rate at which data can be read out in printed form. Similarly,

the rate at which written and pictorial information can t An important object of this invention is to provide a very high speed system for printing alphanumeric, pictorial, or other data from digital logic data.

' Another object is to provide an alphanumeric readout for a high speed digital computer or the like.

Another important object of the invention is to provide such a high speed printer having a cost compatible with the service rendered.

A further object is to provide such a system which is more compact than presently existing slower printers,

and which has a minimum number of moving parts and a long and trouble free life.

' Still another object is to provide a high speed printing device suitable for use as a readout device for large, high speed memories, as'a high speedfacsimile printer, or as a real time pictorial recorder for a television signal or the like.

In accordance with the present invention, these and other objects are accomplished by a rotating drum which carries a plurality of thermal print heads. The thermal print heads extend longitudinally of the drum and are spaced around the periphery of the drum. Each print head includes a matrix of individually controlled hot spots arranged to produce alphanumeric, pictorial-or other information when selectively energized. Each hot spot is controlled by information stored in a serial-to-parallel data converter such as a shift register carried by the rotating drum. A heat sensitive paper is passed around the drum as it rotates, but is in contact only with a portion plied to the drum through any one channel.

Thenovel features believed characteristic of this invention are set forth in the appeded claims. The invention" itself, however, as well as other objects and advantages thereof, may best be understood by reference to the following detailed description of illustrative embodiments, when read in conjunction with the accompanying drawings, wherein:

FIGURE 1 is a schematic side view of a thermal printing device constructed in accordance with the present invention;

FIGURE 2 is a simplified sectional view taken generally on lines 2-2 of FIGURE 1;

FIGURE 3 is a schematic logic and circuit diagram of the thermal printing device of FIGURE 1;

FIGURE 4 is a simplified perspective view of a typical thermal print head used in the device of FIGURE 1;

FIGURES is a simplified sectional view of the thermal print head of FIGURE 4;

FIGURE 6 is a schematic circuit diagram of a heater circuit of the thermal print head of FIGURE 4; and

FIGURE 7 is a schematic logic and circuit diagram of an alternative embodiment of a thermal printing device constructed in accordance with the present invention.

Referring now to the drawings, a thermal printing device constructed in accordance with this invention is indicated generally by the reference numeral 10 in the schematic illustration of FIGURE 1. The printing device 10 is comprised of a'cylindrical drum 12 mounted on a rotating shaft 14. The shaft and drum is driven by some suitable means represented by the motor 16 at a preselected speed. As can be seen in FIGURE 2, a length of heatsensitive paper 18 passes around the cylinder 12 as the cylinder 12 rotates, and is in contact with the cylinder over appriximately 180 of its circumference. The paper 18,may be either a continuous strip, or a series of sheets, and a suitable conventional means is provided to handle the paper.

The particular embodiment of the print head presently to be described is adapted to print lines of alphanumeric characters. This is accomplished by fifty thermal print heads P -P which extend longitudinally of the drum 12 and are equally spaced around the periphery of the drum. Each of 'the fifty print heads P -P is comprised of one hundred twenty alphanumeric character matrices c c (see FIGURE 3), and each of the character matrices is comprised of twenty-five individually controlled hot spots 20. Thus, as illustrated in the schematic logic diagram of FIGURE 3, character matrices C C of print P are designated as 'P C P C the character matrices of print head P are designated as P c, P c, and finally the character matrices of the print head P are designated as P C P C Thus, it will be noted that eachof the print heads. P P has three thousand individually -controllable hot spots 20.

Each of the thermal print heads P P may be fabricated, for example, using the method described in copending US. application Ser. No. 492,174, entitled Thermal Print head, filed on Oct. 1, 1965 by Stephen P.

Emmons et al.. anddassignedto,theassignee of the present I invention. More particularly, each of the hot spots 20 may be comprised of a body of semiconductor material 54 (see FIGURE 5)- covered by a layer of silicon carbide 57. The silicon carbide surface layer 57 is in direct contact with the paper 18 and provides a highly wear re-, sistant surface. Each of the hot spots 20 isheated by a heater circuit, indicated generally by the reference numeral 56 in FIGURE 6, the components of Which are formed by diffusion or other conventional, techniques within the semiconductor bodies 54. The heater circuit 56 is comprised of transistors 58'. and 60: and collector resistors 62 and 64, connected in the conventional man ner illutrated. Thebase 66 of transistor 58 is the control input of the heater circuit. When a logicFO level, i.e., 0.0 volt, is applied to terminal 66, the heater circuitis turned off. When a positive voltage representatiyeof a logic 1 level is applied to the control terminal 66, transistors 58 and 60 conduct, and the current through the transistors and through the collector resistors heats the entire semiconductor body 54 and theoverlying silicon carbide layer 57. The leads interconnecting the transistors and resistors of the heater circuit 56 and the input leads and voltage supplies for the various heater circuits of the matrix may be formed as first and second layer interconnections 68 and 72 formed on oxide layers 70 and 74. Third or fourth level interconnections may, of course, be used if necessary. The structure thus far described is mounted on a ceramic substrate 76 by a suitable bonding material 78, such. as epoxy. The leads to the variousheater elements 56 may then extend down the edge of the ceramic substrate 76, as represented schematically by the structure designated with the reference character 80* in FIG- URE 4. Each adjacent pair "of character matrices, for example matrices P C and P may be separatedby a raised bar 82 formed by semiconductor body 84 and covered by the silicon carbide layer 57.

The print head illustrated in FIGURES 4, and 6 may be fabricated by first etching out grooves in the surface of a semiconductor body to form mesas corresponding to the semiconductor bodies 54 and 84. This maybe accomplished using conventional photolithographic etching techniques, Then the silicon carbide layer 57 is deposited over the surface of the mesas and the grooves. This may be accomplished using, for example, a mixture of tolulene (CH and silicon tetrachloride (SiCl vapors with hydrogen gas as the carrier. These gases, in atypical ratio of about O.87mole percent silicon carbide, 0.18 mole percent tolulene, and the remaining mole percentage hydrogen, are passed over the substrate which is located in a suitable heated furnace and maintained at a temperature of about 1080 C. Next, a layer of polycrystalline or amorphous silicon is deposited over the surface of the silicon carbide layer by the hydrogen reduction of silicon tetrachloride, for example. This layer is not illustrated in the drawings because it is used merely to lend structural rigidity during processing and is subsequently removed. The surface of the semiconductor starting material opposite from the bodies 54 is then removed by lapping and polishing down to the silicon carbide layer 57 previously formed in the grooves. This leaves single crystal semiconductor bodies 54 as islands at the surface of the amorphous silicon body, the silicon islands being isolated from the amorphous silicon body by the silicon carbide layer 57. The silicon carbide layer 57 serves to limit the depth of the lapping and polishing process and assures that the thickness of the semiconductor bodies 54 will be uniform, thus insuring uniform heating and cooling rates for all of the hot spots.

The transistors and. resistors can then be fabricated in the exposed surface of the semiconductor bodies 54 using any standard fabrication technique, and the various lead patterns formed in one or more layers on the surface of the substrate. This structure is then inverted and mounted on the ceramic substrate 76 using-the bonding layer 78,-after which the amorphous layer of silicon'is removed from the silicon carbide layer by a suitable etchant, such as a mixture '-of hydrofluoric acid, nitric acid and acetic acid. During this step of the process, the silicon carbide layer 57 acts as an etch barrier to protect the underlying silicon bodies 2'4,"afld permit the amorphous silicon tobe etched from the grdo've sbe't ween the various hot spots. W

Referring. once again to. FIGURE 3, fifty shift registers DSR -DSR Q, are provided fonthe. fifty print heads P P respectively. In order to have maximum flexibility, each shift register has a three thousand-bit storage capacity, and each bit iscormected to control-one of. the hot spots 20. The shift registers are serial-to-parallel data converters in that three thousandb'its of'bina'ry data may be seriallyfed into-each registerjthen'the. three thousand bits of'data are stored and'converted to three thousand parallel outputs'to control the corresponding hot spots. When-onlyi alphanumeric information is to belprinted by the device 10, only thirty of forty characters will need to be printed by each charactermatrix. The number of bits in theshift registers DSR for each character can then be reduced from twentyfive to about six if anappropriate decoding-circuit is in= cluded to convert the six bit binary code was to control the hot spots of the character matrix in such a manner as to produce the limited number of characters.

The data shift registers DSR DSR are preferably 10- cated adjacent to the print heads P -P substantially'as illustrated in FIGURE 2. The shift registers DSR DSR may be fabricated as integrated circuits occupying about the same volume of space as the print heads P P However, it will be appreciated that as much space as is required within the interior of the drum may be used for the shift registers, ring counter and steering gates presently to be described.

Fifty data gates DG DG and fifty clock gates CG;- CG are sequentially enabled by the outputs from the fifty bits b 42 of a ring counter RC. The ring counter RC is clocked by a low speed clock pulse train applied through slip ring 22 on the shaft 14, the slip ring input being designated by the same reference character in both FIGURES 1 and 3. The frequency of the low speed clock pulse train is equal to the number of data shift registers DSR times the speed of rotation of the drum 12. Thus, if the drumis rotated'at fifty revolutions per second, the low speed clock would have a frequency of 2500 pulses per second. The output from the last bit b of the ring counter-may be fed out through slip ring 24 for synchronization purposes. The

outputs from bits b b of the ring counter RC sequentially enable input data gates DG DG respectively, and high speed clock gates CG CG respectively.

A high speed clock signal is applied to the rotating drum and then to an input of each of the clock gates CG CG through slip ring 26. The frequency of the high speed-clock is at least equal to the product of the total number of storage bits in the fiftydata shift registers DSR DSR and the speed of rotation of the drum 12, plus a slight margin to facilitate operation of the steering logic, as will hereafter be described. Input data is applied to the inputs of data gates DG DG through slip ring 28. .The input data is in serial binary form, and is synchronized with the clock pulses applied through slip ring 26. Thus,the data signal would be at either a logic 0 or a logic 1 level during each of three thousand clock pulses, depending upon the-binary value of the bit. Each successive bit of data is introduced to one end of the shift reg'ister,'then shifted through the remaining'bits of the register. After the three thousandth clock pulse, each of the three thousand bits of-the shift register has the appropriate output, and these outputs are fed in parallel to control the three thousand hot spots-until new data is fed into the shift register.

Electrical power for all of the circuits is applied through slip rings 30 and 32, it being understood that the two slip rings are merely exemplary and that as many slip rings as required can be provided to supply voltage supplies of differ'en't levels.

A pair of timing disks 34 and 36 are mounted on the shaft 14 in order to sense the position and speed of the drum 12 as represented in FIGURE 1. Fifty permanent magnets may be spaced around the periphery of'the disk 34 to induce fifty pulses in the pickup head 38 during each revolution of the drum 12, the magnets preferably being positioned to correspond to the positionof'the print heads P -P5 respectively. The pulse train produced by disk 34 and pickup head 38 may be used to either synchronize or derive the low speed clock pulses used to operate the ring counter RC. A single'r'nagnet may be provided on disk 36 for inducing a single pulse in pickup head 40 during each revolution'of the drum '12. This pulse is used as a reference to determine the position of the drum 12, and from this pulse and the pulses from' output 24, the operation of the ring counter RC is synchronized with the rotation of the drum. Thus, the magnet and pickup head may be located to produce a pulse' when print head P is in the position illustrated in FIGURE 2, for example, indicating that bit b of the ring counter should have a logic 1" output to enable the gates DG and C6 as will--now be described.

The printing device is made compatible with asource of data 44 by an interface 42. The data source may be. any

desired high speed memory, computer, or-other data processing system. The interface 42 takes the data from the source 44 and puts it in digital form suitable for operating the printing device 10, and synchronizes the supply ofdata with the operation of the printing device. The interface may vary widely in design and construction, depending upon the nature of the data provided by-the source, but performs the primary function of supplying thebinary data to be recorded by each of the print heads to the appropriate print head as the print head passes-through the data input are (see FIGURE 2). To this end, the

interface may control the rotation of the drum as represented by line 46 extending to motor 16. Thus, the interface provides an input data signal in theform of three thousand bits of serial data synchronized with three thousand clock pulses within thedesired interval, and insures that the operationof the ring counter is synchronous with the rotation of the drum so that the steering gates DG and C0,, are enabled at the appropriate time. a

In the operation of the device 10, the drum 12 is rotated at some desired constant speed, suchas fiftyrevolutions per second. The ring counter RC would then operate at a rate of twenty-five hundred counts per second; The count ofthe ring counter RC is synchronized with the position of the drum 12 so that the output from bit b enables gates DG and 'CG during the period that print head P passes through the input are 50 equal to no more than one-fiftieth ofone revolution. Thenasprint heads P P etc. successively passthrough the are 50, gates DG and C6 DG3 and C6 etc. are successively enabled by the output from bits b b etc. of the ring counter RC.

Coincident with the enabling of gates DG and CG three thousand bits of serial binarydata are introduced through slip rings 26 and 28 in the'form of-a data signal level synchronized with three thousand clock pulses. The serial data is't-hen stored indata shift register DSR and converted into parallel digital data to simultaneously control the three thousand hot spots 20 of print. head P and form the desired characters within the one hundred twenty character matrices, P C P C As the drum 12 continues to rotate, registers DSR -DSR ,v are sequentially loaded as they pass through the arc 50. During Thus, it will be noted that by using fifty print heads and a drum 'speedof fifty revolutions per second, twentyfive hundredlines per second are printed with each line containing one hundred twenty characters. Of course, this can be increased or decreased as 'desiredby variationsin the 'numberof print heads and in the speed of rotation of the drum. The particular number of print heads and the particular speed of rotation was selected merely as exemplary, and the components herein described for accomplishing' this rate are presently within the state'of the art. p

The rate at which the input data is supplied to the various data shift registers DSR DSR is rather high, being 7.5 million bits per second in the particular embodiment described. Thus, the shift register DSR must operate at a rather high frequency. Ari alternative embodiment of the invention in which the frequency of the input data is reduced is indicated generally by the reference numeral in FIGURE 7. The printing device 100 is very similar to the printing device 10 and corresponding parts are therefore designated bycorresponding reference numerals. The printing device 100 differs from the printing device 10 principally in that five shift registers, each having a six hundred bit capacity, are provided for each of the fifty print heads, rather than a single shift register having a three thousand bit capacity. Thus, data shift registers DSR ,,--DSR control the individual hot spots of print head P data shift registers DSR DSR control the individual hot spots of print head P etc. The shift registers DSR ,.,DSR are simultaneously loaded with data through slip rings 102-106 and data gates DG DG when the gates are enabled by an output from bit b; of the ring counter RC. Similarly, shift registers DSR ,,DS R are simultaneously loaded 'through gates DGg DG when bit b of the ring counter RC has a logic 1 output. Clock gate (36 gates the clock pulse train to all five of the shift registers DSR '-DSR and clock gate CG gates the clock pulse train to-registers DSR -DSR etc.

The operation of the printing device 100 is identical to the operation of the device 10 except that the serial binary input data toeach of the five shift registers for each of the print heads is loaded simultaneously, i.e., in parallel, from the five separate slip rings and steering gates so that the rate at which the data is put into the individual storage means, and thus the rate at which the shift registers must operate, is reduced by one-fifth. It will readily be evident that the'number of shift registers for each print head may be increased or decreased to decrease or increase, respectively, the rate at which data is serially put into the individual shift registers. Thus, in the printing device 100, the data is provided at a rate of 1.5 million hits per second as opposed to 7.5; million bits per second in the printing device 10.

Although the embodiments of the invention herein described have been specifically directed toward printing lines having one hundred twenty alphanumeric characters, it is to be understood that substantially any type of data may be printed in accordance with the broader aspects of the invention. or example, the entire surface of the drum may form a single matrix of hot spots. The matrix may be divided in a convenient manner into two or more sections and one or more shift registers provided for each section. The shift registers for the matrix sections may then be sequentially loaded during the portion of the revolution that the matrix section is not contacting the paper. In the event a plurality of shift registers are used to control each matrix section, the shift registers can be loaded in parallel.

From the above detailed description of the invention, it will be noted that an extremely high speed printer has been described. The printing device is compatible with high speed data processing systems and can be used as the data readout for such systems. The printing device can be used as a high speed facsimile read-out device. By

way of examplejth e device hereindescribed has sufficientspeed capability to record, in real time, the successive fra'mespf conventional television transmission.

What is claimed is: i I I I i 1; A thermal printing device for selectively applying heat to a thermally sensitive membercomprisingz' drum means having a matrix of controllable heating elements formed on the surface thereof for selec- I tively heating predetermined areas on the thermally sensitive member when the predetermined areas are adjacent to said heating elements, means. forrotatingsaid drum means, memory means carried by said ,druin means for re- -ceiving serial data and storing andnconverting the serial datato paralleldata at a plurality of parallel Outputs from said memory means, 1

,the parallel outputs beingconnected to activate associated heating elements in accordance with the data at the respective outputs to produce preselected patterns of heated elements, ,means for supplying the serial data to the memory means during a portion of each.revolution of the drum means as said associated heating elements are being rotated toward a position adjacent the predetermined areas on the thermally sensitive member,

whereby the heating elements are activated in the preselected pattern during the portion of the revolution of the drum means when the heating elements are adjacent the predetermined areas of the thermally sensitive member. 2. In a thermal printing device, the combination of: drum means having a matrix of controllable heating elements formed onthe surface thereof for selectively heating predetermined spots on a heat sensitive sheet disposed adjacent thereto, memory means for receiving serial data and storing and converting the serial data to parallel data at a plurality of parallel outputs, the parallel outputs being connected to activate the heating elements in accordance with the data at the respective outputs, means for rotating the drum means, and means for supplying serial data to the memory means during a portion of each revolution of the drum means whereby the heating elements will be activated in a pattern determined by the data during the remaining portion of the revolution of the drum means such that the pattern may be impressed upon a heat sensitive sheet moving with the drum means adjacent the heating elements during said remaining portion of the revolution, said means for supplying the serial data comprising means for transferring a data signal from a fixed circuit to a circuit rotating with the drum means, gating circuit means carried by the drum means for selectively applying the data signal to the memory means when the gating circuit means is enabled, and

synchronizing circuit means carried by the drum 7 I means and responsive to the position of the drum means for enabling the gating circuit means when said matrix is traversing said portion of each revolution of the drum means. 3. In a thermal printing device, the combination of: drum means having a plurality of matrices disposed at circumferentially spaced points around the periphery thereof, each matrix comprising a plurality of controllable heating elements arranged to produce selected patterns on a heat sensitive sheet disposed adjacent to the matrix, shift register means for each matrix for receiving serial data and storing the data as parallel data appearing at a plurality of parallel outputs from the shift register means, e

circuit means connecting the parallel outputs of the shift regist'enme'ans to'the controllable heating elel ments of therespective matrices for controlling; the heating elements 'of the matrices in "a' manner detera a set of shift register. means for 'minedrby the data at the parallel outputs to produce I I: selected patterns ofheatedelements in the respective Imatrice.-;, .v 1.? r ,.:-Y.-

means for; rotating :the drum. means, and I II means for supplying serial data to the shift register means as the drum means rotates, the serial data being supplied to'feach of the shiftre'gister means i as the matrix controlled by the shift register means I travels through a predetermined portion of a revolution 'fi he d me n i v ,whereby the heating elements will be activated in patterns determined by the data stored in the respective shift register means, and will ,rejrn ainfactivated during th e remaining portion ofthe revolutionof the drum means to impress a pattern upon a heat serrsitive sheet'rotating with thefdrum means adjacent the heating elements during said remaining portion ,of the revolution of the dru'm means, j 4. T l 1e combinationdefined in claim.3wherein th e means for supplying serial data to, the shift register means supplies serial data to a plurality of the shift register means at the same time.

5. The combination defined in claim 3 .wherein the means for supplying serial data to the shift register means comprises: r I v I a data gate carried by the drum means for each shift register. means, each data gate being connected to supply a data signal. to the respective shift register means when enabled, i .first circuit means carried by the drum means for-receiving. a data signal from a source without the drummeans and applying the data signal to each of the data gates,

'' a clock gate carried by the drum means for each shift register means, each clock gate being connected to supply a clock pulse train to the respective shift register means when enabled,

, second circuit means carried by the drum means for a receiving a clock pulse train synchronized with the data signal from a sourcewithout the drum means and applying the clock pulse train to each of the clock gates, and I synchronization circuit means. carried by the drum means and connected to selectively enable each of the gate means, said synchronization circuit means being adapted to receive a synchronization signal related to the rotational position of the drum means and, in response to the synchronization signal, enable the gate means related to the respective matrices as the respective matrices pass through said .predetermined portionof the revolution of. the drum means. r v r 6. In a thermal printing device, the combination of:

a drum means having a plurality of matrices disposed at circumferentially spaced points around the periphery thereof, eachmatrix comprising a plurality of controllable heating" elements arranged to produce selected patterns on a heat sensitive sheet disposed adjacent to the matrix, I a

each matrix, each a shift register means being adapted to receive serial data and store the. data as parallel data appearing at a plurality of parallel outputs from the shift register means, t =-circuit means connecting the parallel outputs of the plurality of.shift register means for. each matrix to the controllable heating elements of the respective matrix for controlling the heating elements in a a manner determined by the'data at the parallel out- ,7 puts of the .shift register means to produce selected :rpatterns of activated, heating elements;inthe respective matrix,

means for rotating the drum means, a set of data gates carried by the drum means for each set of shift register means, each data gate being connected to supply a data signal to one of the shift register means of the set when enabled,

a set of first circuit means carried by the drum means, each of the first circuit means of the set being adapted to receive a data signal from a source without the drum means and apply the data signal to one data gate of each set of data gates,

a clock gate carried by the drum means for each set of shift register means, each clock gate being connected to supply a clock pulse train to each shift register means of a set when enabled,

second circuit means carried by the drum means for receiving a clock pulse train from a source without the drum means and applying the clock pulse train to each of the clock gates, and

synchronization circuit means carried by the drum means, the synchronization circuit means being adapted to receive a synchronization signal related to the rotational position of the drum means from a source without the 'drum means and, in response to the synchronization signal, selectively enable the clock gate and the set of data gates related to the respective matrices as the respective matrices travel through said predetermined portion of the revolution of the drum means.

References Cited UNITED STATES PATENTS 2,715,360 8/1955 Brown 101-92 2,930,347 3/1960 Metzger 178-23 15 2,951,121 8/1960 Conrad 178-3OX RICHARD B. WILKINSON, Primary Examiner.

JOSEPH W. HARTARY, Assistant Examiner.

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